1. Field of the Invention
The present invention relates generally to transmission methods of a wireless communication system, and more particularly, to a method and an apparatus for transmitting and receiving a single data stream through multiple beams in a wireless communication system, which uses hybrid beamforming in which a digital precoder is combined with an analog beamformer.
2. Description of the Prior Art
To meet the demand for wireless data traffic having increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
Data usage amounts in a wireless communication network are increasing exponentially, and thus, mobile communication technology of subsequent generations (e.g., beyond fourth generation (4G)) needs to enable gigabit-class communication, even in an outdoor environment. In this regard, a beamforming technique in a millimeter band is recently attracting public attention as a candidate technique for gigabit-class communication. The millimeter band is advantageous in that the millimeter band can use a wider band than the existing low frequency band, but is disadvantageous in that the millimeter band has large channel attenuation. A beamforming technique can increase the strength of a signal in a particular direction by using multiple antennas. Since a wavelength has been shortened in a high frequency band, multiple antennas can be integrated in a small area. Accordingly, the beamforming technique is again attracting public attention as an important technique that can overcome the problem of the channel attenuation in the millimeter band.
Beamforming may be implemented according to a digital scheme in a baseband, or according to an analog scheme after Digital/Analog (D/A) conversion or at a Radio Frequency (RF) side.
When the beamforming is implemented only according to the digital scheme, it is easy to adjust a beamforming coefficient, namely, the strength and phase of a signal, but an RF path, which is formed by a series of a baseband, a Digital/Analog Convertor (DAC), and an RF side, needs to be disposed for each antenna. Accordingly, this configuration has difficulties relating to costs and implementation.
When the beamforming is implemented only at the RF side, this configuration is low in cost, but may have difficulty providing minute adjustments for the strength and phase of a signal.
Hybrid beamforming corresponds to a structure in which only several RF paths form a baseband and an RF beamformer is combined for each RF path. The hybrid beamforming allows for transmission of multi-data through a digital precoder, and can obtain beamforming gain through an RF beamformer. Accordingly, a hybrid beamforming technique is advantageous in that the hybrid beamforming technique can select a trade-off position appropriate to prepare for the two extremes of beamforming techniques, namely, a case where beamforming is implemented only according to the digital scheme and another case where the beamforming is implemented only according to the analog scheme.